This invention relates to telecommunication access security devices, in particular, to devices which intercept the data provided by the telephone company which identifies the calling party, also known as "Caller ID" or "Calling Number Delivery". The Caller Identification Data (CID) signal parameters and protocol relevant to the present invention are described in the technical advisory entitled, "SPCS-to-CPE Data Transmitter Generic Requirements", Bell Communications Research, TA-NWT-000030, Issue Sep. 2, 1991.
In the prior art, there exists several examples of devices which intercept the CID and utilize the caller's telephone number. One prior art example of such a device is disclosed in U.S. Pat. No. 4,924,496 issued to Figa et al. A method and apparatus of the same nature is described in U.S. Pat. No. 4,582,956 issued to Doughty. More recently, devices and methods intended to be used with a personal computer to provide a display of the caller's number and other information on a personal computer console have been employed. For example, U.S. Pat. No. 5,054,055 issued to Hanle et al. The primary purpose of these devices and methods is to forewarn the called telephone subscriber as to the identity of the caller prior to answering the call, so as to allow the subscriber to make a decision as to whether to accept the call or not, or to provide other information regarding the caller prior to answering the call.
A disadvantage of the devices within the prior art that merely receive and display the CID is that they do not provide means for suppressing the power ring signal of an incoming call until after the CID has been received and processed. Since the data is transmitted by the telephone company between the first and second power ring signals, and only as long as the call is not answered, premature answering of the call during the first power ring will prevent the CID from being transmitted. If the call is answered, whether manually by a person, or automatically by a telecommunication device such as a facsimile machine, modem or answering machine, during transmission of the CID, the transient (i.e., burst of noise) that occurs when the telecommunication device goes to the `offhook` or answer state will interfere with the reception of the data.
Another example of a prior art device by which a caller may be identified, and access to telecommunication devices may be controlled, are those which require the caller to enter access codes via touch tones upon being connected. Prior art examples of this type of device include those disclosed in U.S. Pat. No. 4,937,854 issued to Sarakas and U.S. Pat. No. 4,926,470 issued to Sanford. Disadvantageously, these devices require the cooperation of the caller in order to work, and are easily compromised, i.e., the caller could provide false or stolen information. Another disadvantage of the touch tone access method is that the incoming call is always automatically answered by the device, providing the caller with the opportunity to compromise the security of the system, and requiring that the caller pay for the toll call if such is the case. Another disadvantage of the devices within the prior art is that they do not provide means for selectively passing or blocking the incoming call unattended, based upon the CID provided by the telephone company. Instead, they allow the power ring signal to pass to any telecommunication device which may be connected to the telephone line. The devices of the prior art, therefore, require that a person be present to monitor the caller identification display device in order to make the decision as to whether the call should be accepted or not.
Another disadvantage of the devices within the prior art, particularly those designed to be interfaced to a personal computer, is that they require the use of a limited resource of the computer, to wit, the serial communications interface.
The prior art devices, therefore, have obvious disadvantages and are in fact of little practical usefulness insofar as preventing premature answering of the call to assure reception of the CID, or for providing any reasonable measure of security against unwanted or unauthorized callers to facsimile machines, computers, modems, answering machines, and other telecommunication devices when a person is not present.